Miniature acoustic transducer of improved construction

ABSTRACT

AN IMPROVED TRANSDUCER CONSTRUCTION WHICH INCLUDES A CASE, A BULKHEAD BEING MOUNTED ON THE CASE, AND A COVER IS SECURED TO THE BULKHEAD. A DIAPHRAGM IS MOUNTED ON THE BULKHEAD ADJACENT TO THE COVER. A COIL IS MOUNTED ON THE BULKHEAD WITHIN THE CASE. A U-SHAPED MAGNET SUPPORT IS MOUNTED ON THE BULKHEAD WITHIN THE CASE AND A PAIR OF SPACED MAGNETS IS MOUNTED IN THE CASE, ONE OF THE MAGNETS ON THE BULKHEAD AND THE OTHER ON THE MAGNET SUPPORT. A COIL IS MOUNTED ON THE BULKHEAD ADJACENT TO THE MAGNETS AND A USHAPED ARMATURE REED HAS ONE END CONNECTED TO ONE OF THE MAGNETS THROUGH THE MAGNET SUPPORT AND THE OTHER END OF THE ARMATURE REED EXTENDS THROUGH THE COIL AND IS POSITIONED BETWEEN THE MAGNETS.

Unit atent Inventors Elmer Victor Carlson Prospect Heights; lFloyd Warren Cross, Wheaton; Mend Clifford Killian, Elk Grove Village, 111. App]. No. 9,111 Filed lleb. 9, 1970 Patented June 28,1971 Assignee lndustrial Research Products, llnc. Elk Grove Vlllage, lll. Continuation of application Ser. No. 507,336, Nov. 12, 1965, now abandoned.

MINIATURE ACOUSTIC TRANSDUCER 0F lMlROVED CONSTRUIITlON 8 Claims, 6 Drawing Figs.

1.1.8. 121 179/119A, 179/ 107 lot. (11 r. 110% 11/00 Field 01 Search H 179/1 14 (R), 115 (R), 117, 119 (R), 179, 181

[56] References Cited UNITED STATES PATENTS 3,230,426 1/1966 Sawyer et a1 .1 179/119 Primary Examiner- Kathleen H. Claffy Assistant ExaminerThomas L. Kundert Attorney-Stone, Zummer, Livingston and Aubel ABSTRACT: An improved transducer construction which includes a case, a bulkhead being mounted on the case, and a cover is secured to the bulkhead. A diaphragm is mounted on the bulkhead adjacent to the cover. A coil is mounted on the bulkhead within the case. A U-shaped magnet support is mounted on the bulkhead within the case and a pair of spaced magnets is mounted in the case, one of the magnets on the bulkhead and the other on the magnet support. A coil is mounted on the bulkhead adjacent to the magnets and a U- shaped armature reed has one end connected to one of the magnets through the magnet supportand the other end of the armature reed extends through the coil and is positioned between the magnets.

MINIATURE ACOUSTIC TRANSDUCER OF IMPROVED CONSTRUCTION This application is a continuation of application Ser. No. 507,334, filed Nov. 12, 1965 and now abandoned.

This invention relates to a transducer and more particularly to an improved construction of a transducer which is capable of converting acoustic energy to electric energy and vice versa.

The instant invention relates particularly to an improved transducer which is adapted for use in a hearing aid. Hearing aids have recently achieved a higher degree of acceptance partially because hearing aids have become more cosmetically acceptable. One of the reasons that hearing aids are more cosmetically acceptable is that hearing aid manufacturers have been able to make hearing aids smaller. It is now possible to design and to manufacture a smaller hearing aid because transducers have been madeconsiderably smaller. With the small hearing aid and the small transducer certain problems have been generated. One of the problems with a small transducer is that the transducer requires a high degree of precision. For instance, the tip of an armature reed must be positioned within one micron in the final adjustment.

In order to make a hearing aid minute, a hearing aid designer must make certain compromises. One of the compromises which the hearing aid designer makes is to reduce the amount of shock absorbing material surrounding a transducer in order to reduce the size of the hearing aid, but the likelihood of shock damage to the transducer is increased. At least, one transducer manufacturer has found that between 80 and 90 percent of returned transducers from the field are damaged due to a shock loading on the transducer. It appears that the smaller hearing aids may be readily dropped and are dropped.

It may be appreciated that elderly people have a greater need of hearing aids. Ordinarily, the small hearing aids are worn with the spectacles or are behind-the-ear hearing aids. Inasmuch as elderly people have a lesser degree of manual dexterity and coordination than younger people, an older person is more prone to drop a hearing aid when he is positioning a hearing aid on his head.

In one study which was made to determine the effect of shock on a transducer, it was found that when a transducer is dropped from a height of one meter onto a hard surface, the mean deceleration upon impact was approximately 3000 g., and a high of l5,000 g. was attained. Considering that a small transducer has an approximate weight of 1 gram, it may be stated that the mean force applied to the transducer was approximately 3,000 grams and the maximum force was 15,000 grams. It is, therefore, readily apparent that the high precision construction of a transducer may be readily distorted by dropping it upon a hard surface, such as, a ceramic tiled bathroom floor.

Another problem which is encountered in the manufacture of a minute hearing aid is that the shock absorbing material supporting the transducer may also be used to hold the transducer in position so that there is a static load applied to a transducer housing or casing. This static load has a tendency to strain the housing which may effect the alignment between the magnets and armature.

In the ordinary construction of a transducer, a coil and a pair of magnets is mounted in a case, and an armature reed is mounted in the case and extends through the coil and between the magnets. The armature reed is connected to a diaphragm. In the prior art transducers, the coil and usually one of the magnets is affixed directly to the case. This positioning of the coil and the magnet presents difficulties in positioning accurately the coil and the magnet and also allows the coil and magnet to be dislocated easily due to shock or external loading. Also, it is found that it is particularly desirable to assemble the motor portion of a transducer, that is, the part including the coil, magnets, and armature reed, as a unit which unit may be easily and conveniently mounted in a case.

It is, therefore, a principal object of the instant invention to provide an improved transducer construction wherein the coil, magnets and armature reed are mounted on a bulkhead so that the transducer has a high degree of shock resistance by virtue of. the fact that the coil, magnets and armature reed would move substantially together so that there is little or no relative displacement relative to each other of these parts when shock loading is applied to the transducer.

It is another object of this invention: to provide an improved transducer construction wherein the coil, magnets and armature reed are mounted on a bulkhead, and the bulkhead is mounted in a housing or case so that any static loading on the case does not upset the positioning of the coil, magnets and ar mature reed relative to each other.

It is still another object of the herein disclosed invention to provide an improved transducer construction wherein the coil, magnets and armature reed are mounted on a bulkhead so that the motor portion of a transducer may be assembled as a unit and the motor unit may be easily and conveniently tested and positioned in the case.

It is a still further object of this invention to provide an improved transducer construction in which the construction provides a stiffener plate to cooperate with an armature reed to affect the second mode of vibration of the armature reed.

It is still another object of the present invention to provide an improved transducer construction wherein the transducer may be readily and economically assembled.

Other objects and uses of the subject invention will become readily apparent to those skilled in the art upon a perusal of the following specification in light of the accompanying drawings, in which:

FIG. ii is a perspective view ofa transducer embodying the herein disclosed invention;

FIG. 2 is an exploded cross-sectional view of a case, a bulkhead, and a cover which constitute parts of the transducer shown in FIG. 1',

FIG. 3 is a cross-sectional side elevational view of the transducer shown in FIG. I and taken on line 3-3 of FIG. 1;

FIG. 6 is a cross-sectional end elevational view taken on line 14 of FIG. 3;

FIG. 5 is a cross-sectional view taken on line 5-5 of FIG. 3 showing a plan view of a diaphragm which constitutes a portion of the instant transducer; and

FIG. 6 is a cross-sectional view taken on line 6-6 of FIG. 3 and shows a flared portion ofa reed which constitutes a part of the instant transducer.

Referring now to the drawings and especially to FIG. 3, a transducer I0 being a specific embodiment of the subject in vention is shown therein and generally consists of a case 12 with a motor unit 14 mounted therein, a diaphragm assembly 16 connected to the motor unit M, and a cover 18 connected to the motor unit.

The case 12 is a unitary structure of magnetic material which case includes a rectangular floor 20. The floor has a continuous substantially perpendicular sidewall 22 formed integral with the outer periphery of the floor. A lead aperture 241 is formed in one end of the sidewall as may be best seen in FIG. 3.

The cover lb includes a top 26 which has a sound aperture 28 centrally formed therein. The top 26 is identical in outline to the floor 20 and has a continuous substantially perpendicular edge wall 30 formed integral with the outer periphery of the top so that the edge of the edge wall 30 is registerable with the edge of sidewall 22.

The motor unit M includes a bulkhead 32 which has a flat platform M. The platform has near its center an enlarged aperture 36, and a tube aperture 38 positioned adjacent to one corner as may be best seen in FIG. 5. The platform 341 is mateable with the interior of sidewall 22 and edge wall 30. The platform has a continuous mounting edge 40 formed integral with its outer periphery which edge is substantially perpendicular to the platform and is mateable with sidewall 22. Formed integral with edge s0 is a continuous annular support flange 42 which flange is perpendicular to the mounting edge. As may be ser n in FIG. 3, edge 40 is mateably received within case 12 and the support flange rests on the top edge of sidewall 22. The cover 18 is mounted on top of support flange 42 and the cover mateably receives the platform 34 so that the bulkhead is connected to the cover and the case. A conventional adhesive performs a dual function of securing and sealing the bulkhead to the case and to the cover.

A conventional armature coil 44 is positioned in the aperture 36 with one side in the same plane as the platform and is held therein by a conventional adhesive. Thus, the coil is securely positioned relative to the bulkhead and the platform presents a substantially flat surface adjacent to the cover. The coil, as is conventional, includes a pair of leads 46 and 48 which are electrically connected to the coil and are positioned in aperture 24 to provide a means for conducting electrical current to and from coil 44.

A U-shaped or omega-shaped magnet support 50 is secured to platform 34 adjacent to the coil. The magnet support includes a substantially flat bench 52 which is mounted parallel to platform 34. The bench has a pair of pedestals or arms 54 and 56 formed integral therewith. Formed integral with the other end of the pedestals 54 and 56 are feet 58 and 60, respectively. The feet are secured to the platform adjacent to the mounting edge 40 so that the magnet support is centrally positioned relative to the width of the platform.

As may be seen in FIGS. 3 and 4, a first magnet 62 is adhesively secured to bench 52 of the magnet support. The first magnet is positioned adjacent to the bulkhead. A second magnet 64 is adhesively secured to the platform between the pedestals 54 and 56 and adjacent to the first magnet. The positioning of the magnets as described above provides a conventional magnetic gap 65 for the subject transducer.

A generally Ush'aped armature reed 66 is mounted on the magnet support and has one end magnetically connected to the first magnet through the magnet support. The armature reed 66 extends through coil 44 and has its other end positioned in the magnetic gap. The armature reed includes a flared portion 68 of which the broadest portion is fixed to the bench of the magnet support and is thereby magnetically connected to the first magnet. The flared portion of the armature reed tapers down to a folded portion 70 so that the armature reed folds on itself as may be seen in FIG. 3. Formed integral with the folded portion is a straight portion 72 which extends through the coil 44 and is positioned within magnetic gap 65. A generally rectangular stiffener plate 74 is secured to the flared portion of the armature reed, and the stiffener plate covers a portion of the magnet support as viewed in FIG. 6. The stiffener plate is secured to the flared portion of the armature reed by an adhesive which acts as a visco-elastic material as will be described hereinafter.

. A conventional Thuras tube 76 is connected to bulkhead 32 at tube aperture 38.

The diaphragm assembly 16 includes a surround 78 which is adhesively secured to the platform 34. A diaphragm 80 is mounted within the surround 78 and has a diaphragm aperture 82. Mounted in diaphragm aperture 82 is one end ofa rod or drive pin 84 which has its other endadhesively secured to the straight portion of the armature reed so that the diaphragm is mechanically connected to the armature reed. The drive pin extends through aperture 36 between the coil and magnet 64.

It is evident that the motor unit 14 may be easily and conveniently assembled. Coil 44 is positioned in aperture 36 and is secured to the bulkhead by means of a suitable adhesive. The magnet support 50 is secured to the bulkhead adjacent to the coil, and the magnets 62 and 64 are attached to the magnet support and bulkhead, respectively. The armature reed 66 is attached to the magnet support and is positioned through the coil and in the magnetic gap. The stiffener plate 74 is adhesively secured to the armature reed, and a Thuras tube is mounted on the bulkhead. it is evident that the motor unit may be easily and conveniently tested and adjusted prior to insertion into the case. The object construction of the motor unit has a further advantage in that the major components of the magnetic circuit, such as, the magnets, the magnet support and the armature reed, are not connected directly to the case so that the effect of temperature changes in the case is minimized.

The diaphragm assembly 16 is mounted on the bulkhead and the drive pin 84 is connected to the reed and to the diaphragm. The bulkhead is then positioned in the case 12 and the leads 46 and 48 are positioned in the lead aperture 24. A plate 88 is secured to the sidewall 22 to cover and to seal closed the lead aperture, and in this instance, adhesive 90 is positioned around the leads to hold the leads in position. The cover 18 is adhesively secured to the bulkhead to enclose the diaphragm.

When the transducer 10 is utilized as a microphone or a receiver, sound enters the aperture 28. The sound waves impinge upon the diaphragm to deflect the armature reed since the armature reed is connected to the diaphragm by means of drive pin 84. When the armature reed is deflected, the straight portion of the reed moves closer to one of the magnets and away from the other thereby causing a magnetic flux to flow through the armature reed. Asis conventional, the coil is affected. It should be noted that there are two magnetic flux circuits in the magnet support 50. In one of the circuits, the flux flows through the magnets, a portion of the platform along pedestal 56 and through a portion of the bench 52. in the other circuit, the flux flows through the magnets another portion of the platform along pedestal 54 and through another portion of bench 52.

it is apparent that when the armature reed is closer to one of the magnets, the density of flux between that magnet and the straight portion of the armature reed is increased and a portion of the flux flows along the reed back to the magnet support. lt should be, therefore, noted that by utilizing the subject construction, the magnet support provides an improved flux path without increasing the overall length of the transducer. Furthermore, the instant construction allows that maximum point of displacement of the armature reed to occur in the magnetic gap and still maintain a small minimum overall length of the motor unit. Although the magnetic circuit for the object transducer has been described in terms of a microphone, it is apparent that the operation of a speaker is similar though the source of energy is electrical to operate the diaphragm.

The instant invention provides an additional advantage in that it reduces the secondary mode of vibration of the armature reed without reducing substantially the effective length of the armature reed in its primary mode of vibration. The stiffener plate 74 which is secured to the armature reed by the adhesive is positioned near the node of secondary vibration of the armature reed so that the absorption of vibrational energy by the adhesive is accomplished by virtue of absorption of lateral strain along the length of the armature reed. It is readily apparent that by the absorption of the secondary mode vibrational energy along the axis of the armature reed, the primary mode of vibration is only minimally effected.

Although a specific embodiment of the herein disclosed invention has been described in detail above and shown in the accompanying drawings, it is to be expressly understood that those skilled in the art may make various modifications and changes in the construction shown herein without departing from the spirit and scope of the instant invention. It is to be expressly understood that the present invention is limited only by the appended claims.

We claim:

1. In a transducer the improvement comprising, in combination, a case having a floor and a sidewall formed integral with the outer periphery of said floor, a bulkhead mounted on said case and being sealingly secured to said sidewall, a generally U-shaped magnet support having a pair of arms fixed to said bulkhead within the case, a first magnet secured to the magnet support, a second magnet secured to the bulkhead adjacent to the first magnet to provide a magnetic gap between the magnets, a coil mounted on said bulkhead adjacent to said magnets, and an armature reed connected to the magnet support and extending through the coil and being positioned between the magnets, whereby two magnetic flux paths exist through the magnet support between the magnets with one flux path passing through one arm of the magnet support and the other flux path passing through the other arm of the support.

2. A transducer as specified in claim 1 in which the armature reed is generally U-shaped and has one end mounted on the magnet support, and a stiffener plate is mounted on the armature reed and partially overlaps a portion of the magnet support.

3. A transducer as specified in claim 2 in which a viscoelastic material separates the stiffener plate from the armature reed for absorbing vibrational energy of the armature reed adjacent to magnet support.

4. A transducer as specified in claim l in which the bulkhead includes an aperture and the coil is positioned in the aperture and adhesively secured to the bulkhead.

5. A transducer comprising, in combination, a case including peripheral sidewalls defining an open end, a bulkhead mounted in said case and substantially closing said open end, a magnet stack consisting of spaced magnets forming a working gap therebetween and mounted with the surface of one magnet in engagement with one side of the bulkhead and a second magnet mounted in spaced relation thereto, flux-conductive means connecting said magnets to each other, a diaphragm mounted on the other side of the bulkhead, an opening through the bulkhead, a U-shaped armature having its arms positioned substantially parallel to said bulkhead with one arm relatively further from the bulkhead than a second arm, said one arm being mounted in flux-conductive engagement with one of said magnets, the second arm of the armature extending into the working gap in the magnet stack, and a drive means extending through the opening in the bulkhead and connecting the second arm of the armature to the diaphragm.

6. In a transducer the improvement comprising, in combination, a case including peripheral sidewalls defining an open end, a bulkhead mounted in said case and substantially closing said open end, a diaphragm mounted on said bulkhead, a generally U-shaped magnet support having a pair of arms fixed to said bulkhead, a pair of spaced magnets, one of said magnets being mounted adjacent said bulkhead and the other magnet being mounted on said magnet support, a coil mounted adjacent said bulkhead, a U-shaped armature reed having first and second arms, drive means for connecting said first arm to said diaphragm, said armature being positioned to have its first arm relatively close and substantially parallel to the diaphragm and extending through the coil between the magnets to be movable therebetween, the second armature arm being relatively removed from the diaphragm and being affixed to said magnet support, whereby two magnetic flux paths exist through said magnet support between the magnets, with one flux path passing through one arm of said magnet support, and the other flux path passing through the other arm of said magnet support. I

7. In a transducer as in claim 6 wherein said second arm of said armature is magnetically connected to said magnet sup port externally thereof.

8. In a transducer the improvement as specified in claim 4 wherein a stiffener plate is mounted on said second arm of said armature and partially overlaps a portion of the magnet support. 

